JP2000091161A - Electrolyte for capacitors and capacitors - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolytic solution for a capacitor which is excellent in withstand voltage and charge / discharge cycle characteristics, generates little gas and is excellent in safety, and a capacitor using the electrolytic solution. SOLUTION: A non-aqueous electrolytic solution for a capacitor, comprising an electrolyte solvent containing a phosphate ester represented by the following formula (I) and an electrolyte: (In the formula, R ¹ , R ² and R ³ may be the same or different and are an alkyl group, an unsaturated hydrocarbon group or an aryl group.) And a capacitor using the electrolytic solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION The present invention mainly relates to phosphate ester
Non-aqueous electrolyte for capacitors containing
For more information on non-aqueous electrolytes for capacitors, see
High energy density and excellent withstand voltage and charge / discharge cycle characteristics
Capacitors, especially electric double layer capacitors
To a non-aqueous electrolyte.

[0002]

TECHNICAL BACKGROUND OF THE INVENTION Conventionally, capacitors, especially I
Backup power supply for C and memory, auxiliary / substitute for secondary battery
For electric power with a capacity between the battery and the capacitor
Double-layer capacitors are widely used as low-power DC power supplies
Have been. However, in recent years, camera-integrated VTRs,
New portables such as phones, laptop computers, etc.
With the emergence of electronic devices one after another, such portable electronic devices
Backup to achieve further enhancement of equipment
It is used for power supply and secondary battery
Energy density for electric double layer capacitors
Is required.

[0003] This electric double layer capacitor does not convert a chemical change into electric energy like a storage battery, but utilizes a large capacity of the electric double layer generated at an interface between an electrode and an electrolytic solution to charge the electric charge of the double layer. In and out of the battery in the same manner as charging and discharging of the battery. Such an electric double layer capacitor is composed of two electrodes, a separator, and a generally corrosion-resistant electrolytic solution, and is formed of a material having a large surface area such as activated carbon and a binder such as a fluororesin. Are disposed so as to face each other with a porous separator made of polyethylene or polypropylene interposed therebetween, and the electrolyte solution fills the space between the electrode and the porous separator and the inside of the porous separator.

As an electrolyte for such an electric double layer capacitor, an aqueous electrolyte and an organic solvent (non-aqueous electrolyte) are used. However, the aqueous electrolyte solution has a problem that the withstand voltage is low (about 1.2 V) and it is difficult to obtain an electric double layer capacitor having a high energy density.

On the other hand, an organic solvent-based electrolyte (non-aqueous electrolyte) has a higher withstand voltage than an aqueous electrolyte, so that a capacitor with a high energy density can be obtained.
For this reason, electric double layer capacitors using non-aqueous electrolytes have begun to spread rapidly as backup power supplies for consumer electronic devices.

As such a non-aqueous electrolyte, a mixture of a non-aqueous solvent such as a cyclic carbonate having a high dielectric constant and an electrolyte such as 4-ethylammonium tetrafluoroborate is generally used. However, in such an electrolytic solution, since a cyclic carbonate is used as a solvent, gas generation due to decarboxylation of the solvent at a high temperature is large,
There is a problem that a long-life capacitor cannot be obtained.
In the case where the energy density is significantly increased in the future, the withstand voltage may be insufficient with the above-mentioned electrolyte, and the emergence of a non-aqueous electrolyte having more excellent charge / discharge cycle characteristics has been desired. .

[0007]

The present inventors have sought to solve the problems associated with the prior art as described above. An object of the present invention is to provide a non-aqueous electrolytic solution for a capacitor which generates less gas, has excellent withstand voltage and charge / discharge cycle characteristics, and is excellent in safety, and a capacitor using the same.

[0008]

The non-aqueous electrolyte solution for a capacitor provided by the present invention comprises a non-aqueous electrolyte solvent containing a phosphate ester represented by the following formula (I) and an electrolyte. I have.

Embedded image (In the formula, R ¹ , R ² and R ³ may be the same or different and are an alkyl group, an unsaturated hydrocarbon group or an aryl group.) The non-aqueous solvent is represented by the formula (I) It may be a mixture of the represented phosphoric acid ester with another solvent, for example, a mixed solvent with a cyclic carbonate. The present invention is also characterized by providing a capacitor using the above non-aqueous electrolyte for a capacitor.

The non-aqueous electrolytic solution for a capacitor according to the present invention comprises:
Low gas generation, high withstand voltage, excellent safety and charge / discharge cycle characteristics. In particular, when a capacitor is formed using the non-aqueous electrolytic solution for a capacitor according to the present invention, a high voltage can be generated, gas generation is small, a charge / discharge cycle characteristic is excellent, and a capacitor having a high energy density is obtained. In particular, when it is used for an electric double layer capacitor, the effect is remarkably exhibited.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the non-aqueous electrolyte solution according to the present invention
The capacitor and the capacitor will be specifically described. Nonaqueous Electrolyte Solution for Capacitor The nonaqueous electrolyte solution according to the present invention is a nonaqueous electrolyte solution represented by the following formula (I).
An electrolyte solvent containing an acid ester and an electrolyte
You.

Phosphate ester First, the phosphate ester represented by the formula (I) will be described.

Embedded image In the formula (I), R ¹ , R ² and R ³ may be the same or different and are an alkyl group, an unsaturated hydrocarbon group or an aryl group. As the alkyl group, an alkyl group having 1 to 4 carbon atoms is preferable. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, and an n-
Butyl group, i-butyl group, sec-butyl group and t-
Butyl groups can be mentioned. As the unsaturated hydrocarbon group, an unsaturated hydrocarbon group having 2 to 4 carbon atoms is preferable, and examples thereof include a vinyl group, an allyl group, and an isopropenyl group. The aryl group is preferably an aryl group having 6 to 12 carbon atoms, and examples thereof include a phenyl group, a benzyl group, a naphthyl group, and a biphenyl group. In the present invention, in the above formula (I),
R ^{1 to} R ³ may be the same or different, but are preferably the above-mentioned alkyl group or unsaturated hydrocarbon group,
Further, R ^{1 to} R ³ are each independently, more preferably all are the same, and —CH ₃ , —C ₂ H ₅ and —CH ₂
It is preferably selected from among -CH = CH _2.

Specific examples of such a phosphate ester include trimethyl phosphate, triethyl phosphate, diethylmethyl phosphate, ethyldimethyl phosphate, tripropyl phosphate, tributyl phosphate, triallyl phosphate, and allyl phosphate. Dimethyl and the like.

In the present invention, in the above formula (I), R ^{1 to} R ³ are all the same, and CH, C ₂ H ₅ and CH ₂ —CH =
Trimethyl phosphate, triethyl phosphate, and triallyl phosphate, which are groups selected from CH ₂ , are preferable, and trimethyl phosphate and triallyl phosphate are particularly preferable. The phosphate ester of the present invention may be used alone or in combination of two or more. The phosphoric acid ester represented by the formula (I) has excellent acid resistance, is not oxidized even when left in the air, is chemically stable, and is water-stable under ordinary storage conditions. It does not react or react with highly reactive substances such as metallic lithium. Further, such phosphorus carbonate is physically safe, hardly thermally decomposed, flame-retardant, and hardly subjected to electrochemical oxidation and reduction.

Electrolyte Solvent In the present invention, a solvent containing the above-mentioned phosphate ester is used as the non-aqueous electrolyte solvent. Such a non-aqueous electrolyte solvent may be a single solvent of the phosphate ester or a mixed solvent with another solvent.

Other solvents include ethylene carbonate (1,3-dioxolan-2-one), propylene carbonate (4-methyl-1,3-dioxolan-2-one) and butylene carbonate (4,5-dimethyl-one). Cyclic carbonates such as 1,3-dioxolan-2-one) and vinylene carbonate,
Dimethyl carbonate, methyl ethyl carbonate,
Diethyl carbonate, methyl propyl carbonate,
Chain carbonates such as methyl isopropyl carbonate, cyclic esters such as γ-butyrolactone, γ-valerolactone, 3-methyl-γ-butyrolactone, 2-methyl-γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, methyl acetate, and ethyl acetate , Propyl acetate, methyl propionate,
Chain esters such as methyl butyrate and methyl valerate, 1,4-
Dioxane, 1,3-dioxolan, tetrahydrofuran,
Cyclic ethers such as 2-methyltetrahydrofuran, 3-methyl-1,3-dioxolane, 2-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane,
Examples thereof include chain ethers such as diethyl ether, dimethyl ether, methyl ethyl ether and dipropyl ether, and sulfur-containing compounds such as sulfolane.

As the cyclic carbonic acid ester, in addition to the cyclic carbonic acid ester exemplified above, a cyclic carbonic acid ester having a halogen atom-substituted alkyl described in JP-A-9-63644 can be used. Examples of such a cyclic carbonate include monofluoromethylethylene carbonate, difluoromethylethylene carbonate, trifluoromethylethylene carbonate and the like. Of these solvents, cyclic carbonates are preferred. These solvents can be used alone or in combination of two or more.

In the present invention, when a mixed solvent of the phosphate represented by the formula (I) and another solvent is used as the electrolyte solvent, the phosphate represented by the formula (I) and the cyclic carbonate are used. And a mixed solvent thereof is preferred. In such an electrolyte solvent, the phosphate represented by the formula (I) is contained in an amount of 0.1% by weight or more, particularly 0.5% by weight to 100% by weight, based on the total amount of the electrolyte solvent. Is preferred.

Electrolyte The electrolyte contained in the non-aqueous electrolyte for an electric double layer capacitor according to the present invention is, specifically, tetrabutylammonium tetrafluoroborate ((C ₄ H ₉ ) ₄ NBF ₄ ), 4-ethylammonium borate ((C ₂ H ₅ ) ₄ NBF ₄ ), 4
3-ethyl 1-methyl ammonium fluoroborate ((C
_{2 H 5) 3 (CH 3} ) NBF 4), 6 hexafluorophosphate 4-butylammonium _{((C 4 H 9) 4} NPF 6), 6 hexafluorophosphate 4
Ethyl ammonium ((C ₂ H ₅ ) ₄ NPF ₆ ), 3 ethyl 1-methyl ammonium hexafluorophosphate ((C ₂ H ₅ ) ₃ (C
Ammonium salts such as H ₃ ) NPF ₆ ), tetrafluoroboric acid 4
Butyl phosphonium _{((C 4 H 9) 4} PBF 4), 4 fluoride borate tetraethyl phosphonium _{((C 2 H 5) 4} PBF 4),
4-butylphosphonium hexafluorophosphate ((C ₄ H ₉ ) ₄ P
PF ₆ ), 4-ethylphosphonium hexafluorophosphate ((C ₂
H _{5) 4} PPF ₆₎ phosphonium salts such as, International Publication No. W
Examples of the electrolyte include those commonly used in electrolytes for electric double layer capacitors, such as the electrolyte described in O95 / 15572. These electrolytes can be used alone or in combination of two or more. Of these, (C ₄ H ₉ )
_{4 NBF 4, (C 2 H} 5) 4 4NBF 4, (C 2 H 5) 3 (CH 3)
NBF ₄ is preferably used.

The non-aqueous electrolyte of the present invention can be obtained by dissolving the above-mentioned electrolyte in the above-mentioned electrolyte solvent.
It is desirably contained in an amount of 0.5 mol / l, preferably 0.5 to 1.5 mol / l.

Since the non-aqueous electrolyte for an electric double layer capacitor according to the present invention contains the phosphoric ester represented by the above formula (I), it generates less gas, has a high withstand voltage, and has high charge-discharge cycle characteristics. Is excellent. In addition, the non-aqueous electrolyte according to the present invention has a higher flash point and higher safety than solvents such as 1,3-dioxolane, tetrahydrofuran, and 1,2-diethoxyethane that have been conventionally used for the electrolyte. ing. In addition, when (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ is used, high electric conductivity can be obtained. Therefore, when the nonaqueous electrolyte for an electric double layer capacitor according to the present invention is used, it is possible to obtain an electric double layer capacitor that is safe with little gas generation, has a high withstand voltage, and has excellent charge / discharge cycle characteristics.

Capacitor The electric double layer capacitor is composed of two electrodes, a separator and a generally corrosion-resistant electrolytic solution, and two electrodes are arranged so as to face each other with a separator interposed therebetween. An electrolytic solution fills the space between the porous separator and the inside of the porous separator. As the electrode, an electrode formed of a material having a large surface area such as activated carbon and a binder such as a fluororesin is preferably used.

Activated carbon is preferable as the electrode material. Examples of the activated carbon include phenol-based, pitch-based, polyacrylonitrile-based and coconut husk-based fibrous or powdered materials, and usually have a specific surface area of 1000 m ² / g
The above are preferred. The activated carbon activation method is
A steam activation treatment method and an alkali activation treatment method are exemplified.

Examples of the binder include carboxymethylcellulose, polyvinylidene fluoride, polyvinylpyrrolidone,
Examples include polyimide, polyvinyl alcohol, and polyacrylic acid. Further, it is usually preferable to use the electrode in combination with the above-mentioned electrode material (active material) and a current collector. As the current collector, for example, an aluminum foil is preferably used. Preferred examples of the separator include a porous film made of polyethylene or polypropylene.

A specific example of the electric double layer capacitor will be described below with reference to the drawings. FIGS. 1 and 2 show the configuration of a wound type electric double layer capacitor element in Examples 1 and 2 of the present invention and Conventional Example 1, and a state in which this capacitor element is integrated with a sealing member and inserted into a metal case. 1 and 2, reference numeral 1 denotes a capacitor element, and the capacitor element 1 has an anode-side polarizable electrode 3 to which an anode-side lead wire 2 is connected and a cathode-side polarizability to which a cathode-side lead wire 4 is connected. An electrode 5 and a separator 6 therebetween.
And is wound by interposing. A sealing member 7 made of rubber is attached to the anode-side lead wire 2 and the cathode-side lead wire 4 of the capacitor element 1.
Further, this capacitor element 1 is impregnated with a driving electrolytic solution, and then housed in a bottomed cylindrical metal case 8 made of aluminum. With this storage, the metal case 8
The sealing member 7 is located at the opening of the metal case 8, and the opening of the metal case 8 is sealed by performing horizontal drawing and curling on the opening of the metal case 8. The part is sealed.

In the above description, the wound type electric double layer capacitor has been described.
Patent Application Publication No. JP-A-8-78291 discloses a coin-type electric double-layer capacitor and a multilayer electric double-layer capacitor described in JP-A-8-78291. Similar effects can be obtained by using the electrolytic solution of the present invention.

[0026]

【Example】 Hereinafter, the present invention will be further described based on Examples.
Although the present invention will be described in detail,
There is no limitation.

Example 1 2.71 g (0.0125 mol) of tetraethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ) was dissolved in trimethyl phosphate to prepare 25 ml of a non-aqueous electrolyte. (Electrolyte concentration 0.5 mol / l). The withstand voltage of the obtained electrolyte was measured. Further, using the non-aqueous electrolyte solution obtained above as the electrolyte solution, as a polarizable electrode, acetylene black to coconut shell-based activated carbon powder, acetylene black, a slurry obtained by dispersing a mixed powder in carboxymethylcellulose in water roughened aluminum A 2.3V30F rated electric double-layer capacitor (φ18mm × L40m) shown in FIG. 1 was used by using a product coated and dried on a foil and using a polypropylene non-woven fabric as a separator.
m) was prepared, and a charge / discharge test was performed.

In the present application, the evaluation of the withstand voltage of the electrolytic solution and the charge / discharge test were carried out as follows. Table 1 shows the results
Shown in Withstand voltage: The electrolytic solution was placed in a three-electrode withstand voltage measuring cell using a glassy carbon electrode as a working electrode and a counter electrode and an Ag / Ag + electrode as a reference electrode, and a potential of 10 mV / sec with a potentiogalvanostat. , And a range in which the oxidation-reduction decomposition current did not flow 1 μA or more with respect to the Ag / Ag + electrode was defined as the withstand voltage. Charge / discharge test: A charge / discharge test was performed in which the process of charging to a charge end voltage of 3.5 V at a charge current of 3 A and discharging to a discharge end voltage of 1.5 V at a discharge current of 3 A in an environment of 70 ° C. was one cycle. . Under these conditions, the amount of change in height of the wound electric double layer capacitor after 10,000 cycles was measured.

Example 2 2.71 g (0.7%) of ₄ -ethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ) was added to a mixed solvent obtained by mixing trimethyl phosphate and propylene carbonate at a weight ratio of 1: 1. 0
125 mol) to prepare a 25 ml non-aqueous electrolyte (electrolyte concentration: 0.5 mol / l). The withstand voltage of the obtained electrolyte was measured in the same manner as in Example 1. The withstand voltage of the obtained electrolyte was measured. Further, in the same manner as in Example 1 using the electrolytic solution of Example 2,
Rated 2.3V30F wound electric double layer capacitor (φ
18 mm × L40 mm) and a charge / discharge test was performed. Table 1 shows the results.

Example 3 2.71 g (0.0125 mol) of tetraethylammonium tetrafluoroborate (((C ₂ H ₅ ) ₄ NBF ₄ ) was dissolved in triallyl phosphate, and 25 ml of a non-aqueous electrolyte was added. The withstand voltage of the obtained electrolytic solution was measured in the same manner as in Example 1. Further, using the obtained electrolytic solution, a wound electric double layer having a rating of 2.3V30F was produced in the same manner as in Example 1. A capacitor (18 mm × L40 mm) was prepared and subjected to a charge / discharge test, and the results are shown in Table 1.

Example 4 Triallyl phosphate was added to 3-ethyl 1-methyltetrafluoroborate
Nmonium ((C_TwoH_Five) _Three(CH_Three) NBF_Four2.54g
(0.0125 mol) and 25 ml of non-
A water electrolyte was prepared. Example 1 about the obtained electrolytic solution
The withstand voltage was measured in the same manner as described above. In addition, the resulting electrolysis
2.3V30F rated in the same manner as in Example 1 using the liquid
Wound electric double layer capacitor (φ18mm × L40m
m) was prepared, and a charge / discharge test was performed. The results are shown in Table 1.
You.

Comparative Example 1 An electrolytic solution was prepared in the same manner as in Example 1, except that propylene carbonate was used instead of trimethyl phosphate. Further, using the obtained electrolyte solution, a wound electric double layer capacitor (φ18 mm × L40 mm) having a rating of 2.3 V30F was prepared in the same manner as in Example 1, and a charge / discharge test was performed. Table 1 shows the results.

[Table 1]

From Table 1, it can be seen that the electrolyte solutions of Examples 1, 2, 3, and 4 have a higher withstand voltage since the electrolyte solution of Comparative Example 1 has a larger potential difference from the oxidation potential to the reduction potential. Furthermore, the wound electric double layer capacitors using the electrolytes of Examples 1, 2, 3, and 4 were higher than the wound electric double layer capacitors using the electrolyte of Comparative Example 1 after the charge / discharge test. Since the change in the resistance is small, it is understood that the use of the electrolytic solution of the present invention makes it possible to form an electric double layer capacitor that generates less gas, has a high withstand voltage, and has excellent cycle characteristics.

In the above description, the nonaqueous electrolytic solution for a capacitor has been described by taking an electric double layer capacitor as an example.
The present invention is not limited to this, and similar effects can be obtained even when used for an aluminum electrolytic capacitor.

[0035]

As described above, the present invention provides a non-aqueous electrolyte which is capable of producing a capacitor which is low in gas generation, excellent in withstand voltage and charge / discharge cycle characteristics, and excellent in safety. And provide excellent capacitors using it

[0036]

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a configuration of a capacitor element of a wound electric double layer capacitor according to the present invention.

FIG. 2 is a perspective view showing a state where the capacitor element of FIG. 1 is integrated with a sealing member and inserted into a metal case.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capacitor element 2 Anode side lead wire 3 Anode side polarizable electrode 4 Cathode side lead wire 5 Cathode side polarizable electrode 6 Separator 7 Sealing body 8 Metal case

Continuing on the front page (72) Inventor Tsuneaki Koike 3-2-5 Kasumigaseki, Chiyoda-ku, Tokyo Mitsui Chemicals, Inc. (72) Inventor Hideki Shimamoto 1006 Kazuma Kadoma, Kazuma, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. (reference) 5H029 AJ05 AM03 CJ02 CJ22 DJ09 EJ12 HJ02

Claims (8)

[Claims] 1. A non-aqueous electrolyte solution for a capacitor, comprising an electrolyte solvent containing a phosphate ester represented by the following formula (I) and an electrolyte. (In the formula, R ¹ , R ² and R ³ may be the same or different and are an alkyl group, an unsaturated hydrocarbon group or an aryl group.) 2. The phosphoric ester represented by the formula (I), wherein R ¹ , R ² and R ³ are an alkyl group having 1 to 4 carbon atoms, an unsaturated hydrocarbon group having 2 to 4 carbon atoms or a carbon number. The non-aqueous electrolyte for a capacitor according to claim 1, wherein the group is 6 to 12 aryl groups. 3. The phosphoric ester represented by the formula (I), wherein R ¹ , R ² and R ³ are CH ₃ , C ₂ H ₅ and CH ₂ -C
_2. A method according to claim 1, wherein H is selected from CH2.
3. The non-aqueous electrolyte for a capacitor according to item 1. 4. The non-aqueous solution for a capacitor according to claim 1, wherein the electrolyte solvent is a mixed solvent of a phosphate ester represented by the formula (I) and a cyclic carbonate. Electrolyte. 5. A capacitor using the non-aqueous electrolyte for a capacitor according to claim 1. 6. The capacitor according to claim 5, wherein the capacitor is an electric double layer capacitor. 7. A capacitor comprising an anode-side polarizable electrode, a cathode-side polarizable electrode, a separator and an electrolytic solution, wherein the polarizable electrode is an electrode using activated carbon powder as an electrode material, and the electrolytic solution comprises: An electric double layer capacitor which is the electrolytic solution according to any one of claims 1 to 4. 8. The electric double layer capacitor according to claim 7, wherein the polarizing electrode is formed by applying a mixed powder obtained by adding acetylene black and carboxymethylcellulose to activated carbon powder on a current collector foil and drying the powder.